1. Field of the Invention.
The present invention relates to temperature control apparatus. In particular, the present invention relates to a computer controlled digital thermostat.
2. Description of the Prior Art.
With the dramatic increase in energy costs in recent years, and the growing concern over the availability of fuels, increased attention has been focused upon energy conservation. The reduction of energy consumption in home heating has been a topic of widespread interest.
Significant energy saving in home heating can be achieved by the use of temperature setback at one or more periods during each day. For example, by decreasing the control temperature setting of a thermostat during sleeping hours and during times of day when no one is at home, significant energy savings can be achieved. Clock thermostats which provide at least one setback period have been available for many years. Until recently, these clock thermostats have generally been of a mechanical or electromechanical type.
With the recent development of microprocessors and microcomputers, computerized thermostats which automatically provide two or more setback and setup temperature periods have been developed. Among manufacturers of computerized thermostats are Autotronics, Inc., Control Pak Corporation, Honeywell, Inc., Micro Display Systems, Inc., PSG Industries, Inc., RapidCircuit Corp., and Texas Instruments. A description of computerized thermostats available from these manufacturers may be found in Popular Science, "Computerized thermostats program your comfort and save on energy costs", pages 104-106 (October 1979).
Other digital thermostats or process control apparatus are disclosed in the following U.S. patents:
______________________________________ Bunting U.S. Pat. No. 3,912,913 Stephenson 4,001,557 Marooka et al 4,004,138 Hall 4,071,745 Wong 4,079,366 Wyland 4,110,632 Balduzzi et al 4,162,036 ______________________________________
In Bunting U.S. Pat. No. 3,912,913, a process control apparatus is disclosed which includes a digital computer. Digital temperature values from a temperature register are compared with values from a temperature sensor. A program which may be coded on a punch card or tape is read by a program reader and is used to control the arithmetic unit and provide selection of the proper temperature from the temperature register at the appropriate times.
The Stephenson U.S. Pat. No. 4,001,557 shows a digital process controller having a timing clock which is used in conjunction with programmable read only memories. A specific embodiment shown by Stephenson shows temperature being varied as a function of time, together with auxiliary control of a vacuum pump and a gas pump.
In the Marooka et al U.S. Pat. No. 4,004,138, a temperature control for a steel furnace is shown. The control utilizes various arithmetic units and a temperature decision unit to control temperatures in various zones of the steel furnace.
The Hall U.S. Pat. No. 4,071,745 shows a microprocessor controlled electronic thermostat. The values of the reference temperatures and times are programmable and changeable by the user. In addition, hysteresis and anticipation values are stored. Zone control of multiple zones is also illustrated in the Hall patent.
The Wong U.S. Pat. No. 4,079,366 shows a digital thermostat which includes digital memories, a keyboard and a display. The user may program in any desired temperature and time. Hysteresis is adjustable in the digital thermostat of the Wong patent. In addition, day off selectors are provided so that weekends can have a different time/temperature program.
The Wyland U.S. Pat. No. 4,110,632 shows a device which monitors indoor and outdoor temperatures together with a time count from a seven-day counter. The purpose of the device is to disconnect selective loads when conditions of peak electrical use are likely to occur.
The Balduzzi et al U.S. Pat. No. 4,162,036 shows a solid state thermostat having a pair of potentiometers R.sub.d and R.sub.v controlled by knobs 13 and 14 to provide set points for high and low temperatures. One or the other of these two potentiometers is switched into a bridge by switches S1 and S2. These switches are controlled by flipflop FF4, which in turn is controlled by Clock 1 and Clock 2. When one of the clock settings is reached, it triggers FF4 which in turn selects the appropriate switch S1 or S2.
Although there has been considerable recent activity in the development of digital computerized thermostats, there is a continuing need for improvement. In particular, the computerized thermostats which have previously been available have been rather costly. In addition, programming of the digital computerized thermostat has often been complex, and has required a large number of buttons or keys in order to enter, store, and recall time and temperature settings.